(1) Field of the Invention
This invention relates to an aqueous matte coating composition.
(2) Description of the Prior Art
An aqueous coating composition has widely been used, because it uses water as a medium and is free of troubles about working atmosphere, danger of fire, and so forth. However, recent diversification in user's need shows a tendency to lose interest in feeling of metallic luster and highly demands matte coated film which provides grave feeling.
In fact, some aqueous matte coating compositions such as those prepared by incorporating an inorganic silica matte pigment or an organic fine powder of polyethylene, fluorocarbon resin or the like into the aqueous coating compositions have already been proposed.
However, the above aqueous matte coating compositions in the prior art all have such drawbacks that these coating compositions have poor stability and coated film obtained therefrom has poor durability because of sedimentation or floating of the pigment or fine powder in the aqueous coating composition.
In addition to the above aqueous matte coating compositions, a coating composition prepared by incorporating fine particles of an internally crosslinked resin thereinto has also been proposed without being practically used because it has such drawbacks that its matte effect is unsatisfactory and so forth.
Further, the present inventors proposed a process for forming a matte film by use of an anionic electrodeposition coating composition comprising a vinyl copolymer containing an alkoxysilane group as a basic resin and an amino resin as a curing agent (see Japanese Patent Publication No. 24519/87).
The aqueous matte coating composition used in the above process is such that the acrylic copolymer used as the basic resin has alkoxysilane group on its side chain and the alkoxysilane group is gradually hydrolized on water solubilization or making water dispersion to form silanol, i.e. Si--OH and further condensation between the silanols forms Si--O--Si linkage, resulting in forming fine dispersion particles having an interparticle gel structure. As the result, when the fine dispersion particles are subjected to anionic electrodeposition coating, a film having a fine coarse surface is formed and even if heat-cured, the film keeps the coarse surface without forming a complete melt flow to form a good matte film, resulting in being widely used in the art.
However, application of the above aqueous matte coating composition to other coating methods such as spray coating, dip coating, brushing and the like than electrodeposition coating results in forming no fine coarse surface on carrying out coating and in providing unsatisfactory matte effects.
On the other hand, when the above aqueous matte coating composition is subjected to the above anionic electrodeposition coating, a remaining coating liquor on the film after coating causes to partly dissolve the fine coarse surface, resulting in producing uneven gloss after heat-curing. This requires a step of washing with water after carrying out electrodeposition coating. Therefore, from the standpoint of productivity, development of an electrodeposition coating composition, which does not require the step of washing with water, is highly demanded.